Beginning in 1995 the GFDL Hurricane Prediction System has provided operational guidance for more than 300 storm cases in the Atlantic. Relative to the other guidance of the National Weather Service, the
mean GFDL track forecasts appear to be significantly superior after the first day. Nevertheless, the GFDL Hurricane Prediction system exhibits small track biases and rather large intensity biases. For the most part, the nested GFDL Hurricane Prediction System has been utilized with its standard three mesh model resolutions of 1, 1/3, and 1/6 deg. for both operational and research use. In the past several years, the resolution of global models have increased such that they are comparable if not finer than the outermost mesh of the GFDL model. Recently NCEP has upgraded the resolution of their global forecast/analysis system to T170/L42. It is known that the storm track is primarily controlled by the environmental winds resolved by the global model analysis and subsequently used in the outer mesh of the GFDL analysis. It may be that finer resolution of the GFDL model in the outermost mesh will further improve track prediction. In addition, a lack of finer resolution in the storm region has caused maximum winds to be under forecast for hurricanes stronger than 90 knots even when model surface pressures fall below 930hPa. This can be seen by analyzing the GFDL model pressure-wind relationship relative to that observed. Therefore an increase in the inner mesh resolution may reduce this bias for strong storms and therefore increase skill in intensity forecasts.
A set of sensitivity experiments have been initiated to study the impact of resolution on track and intensity forecasts of the GFDL model. An upgrade of the 3-nest system is underway in which the model
resolution is increased to 1/2, 1/4, and 1/8 deg. Improvements in track forecasts due to the doubling of resolution in the outer regions of the storm and improvements in intensity forecasts due to the increased resolution near the storm are anticipated. A suite of sensitivity experiments will be run with this new domain configuration and the results will be presented. The computational overhead for this grid configuration should be ~ 4 times than that of the standard grid configuration. Other grid configurations may also be tried including
a doubling of the standard resolution for each mesh (an overhead of ~8) or adding a fourth mesh of 1/12 deg. to the standard grid configuration (an overhead of ~2). Consideration will be made to running further experiments using these or other grid configurations as well as increasing the vertical resolution of the GFDL 18 level model. These grid configurations are now computationally feasible in research mode and should be feasible operationally in the near future